You can check display unit operations with the PLC, without actually connecting the PLC.
This feature is useful in checking and debugging the display unit after changes in PLC device values.
From PLC manufacturer's simulation software (referred to as "external PLC simulator") change PLC device value
On the computer, after changing a device value, you can check display unit operations
33.5.3 Procedure - Checking Display Unit operation and PLC interaction on the Computer